Whenever the sum of all electrical power supplied to an electrical power grid by energy suppliers falls short of the sum of all electrical power extracted from the grid by customers, there is a danger that the grid supply becomes unstable and eventually breaks down. An overabundance of power supplied to the grid may also be detrimental, because it may cause electrical parameters, such as the grid voltage or the frequency to change. The amount of power supplied to the grid may vary depending on the season, and also depending on the time of day. For example, energy generators producing renewable energy, such as wind or solar farms, may produce much lower power levels during certain seasons or during certain times of day. On the other hand, there is also the variance in the demand of electrical power from the grid by the consumers, also depending on the season as well as on the time day. For example, power hungry air-conditioners may be utilized mainly during hot summer months.
In order to be able to ensure a stable supply of power to all customers, the provider of an electrical power grid will have to install some sort of power management. This includes long-term management in order to anticipate seasonal changes in the supply and demand of electrical power, and short-term management, which reacts to changes in supply and demand in a matter of hours, minutes, or even seconds.
One approach for such management is to control the loads connected to the grid. This is called load management or demand side management (DSM). In this case, customers of the grid relegate some of their command over their power consuming appliances and systems to the management system, which can decide on the amount of power consumed by each appliance at a certain time, within predefined decision making boundaries. For example, a customer may program an appliance, such as a washing machine, to start a process any time during a certain day or during a certain time period. The management system may then be given permission to control the exact time when the appliance starts that process within that day or time period, depending on when the grid can supply the necessary electrical power to the appliance. The appliance can even be used by the management system to syphon off excess electrical power from the grid when necessary.
On the other hand, power station management or supply side management may be employed. In this case, instead of controlling the loads, the management system will regulate the output provided by the power stations supplying the power to the grid, in order to avoid a power shortage on the grid. In particular, the management system might decide to turn on a power plant using a conventional fossil fuel based energy source at times when renewable energy sources are not able to supply enough power to the grid.
The arrival and rise of renewable energy sources has lead to a certain degree of decentralization of the energy market. One of the incentives for this decentralization is the possibility to sell electrical power generated by small renewable energy sources to the grid power provider. Specifically, a customer of the electrical grid, i.e. anyone who is running appliances with electrical power from the grid, may install a solar panel next to his or her building. The solar panel will provide electrical energy to the appliances of the customer, leading to reduced electrical bills. When the solar panel does not produce enough energy to run all the appliances, the customer might choose to either reduce the number of loads on his side, or to use more electrical power from the grid in order to satisfy his energy needs.
Often, the customer installing and operating such a local power source or local power generator, will also install a battery system nearby, which will store any excess energy coming from the local power generator during peak production times, such as on windy hours for a wind turbine or during especially sunny periods for solar panels, which the appliances cannot absorb at that time. Instead, this stored energy can be used at a later time, when there is not enough power being generated by the local power source to supply to the appliances. In addition, when there is no excess power to charge it, such a battery system may also be charged with electrical power coming from the external grid.
Besides selling the power generated by his local power generator directly to the grid power provider, the customer can sell some of the electrical energy stored in the battery system to the grid power provider. However, since the customer usually does not know the status of the grid at any given time, he will not know when would be an ideal time to supply the electrical power from the battery system to the external grid.
It is therefore one objective of the present invention to provide devices and methods for managing a battery system installed at a building of a customer and connected to an external power grid, in such a way as to efficiently and safely supply electrical power to the external power grid.